Effect of laser shock peening on near-surface residual stress and microstructure of laser additive manufacturing AlSi10Mg alloy

Abstract

This study investigates the effects of variations in laser shock peening (LSP) energy on the near-surface residual stress distribution and microstructural evolution of laser additive manufacturing (LAM) AlSi10Mg components, with the aim of evaluating and optimizing LSP processes. Near-surface residual stress was non-destructively tested through an innovative application of the Short Wavelength Characteristic X-ray Diffraction technique (SWXRD). Compressive residual stress predominated within the 2.0 mm thick after LSP, reaching maximum values of −95.9 MPa (15 J) and −103.6 MPa (30 J) at a depth of 0.6 mm, exhibiting a spoon-shaped profile. Surface hardness increased by 24 % (15 J:136 HV) and 35 % (30 J:149 HV) compared to the untreated sample (114 HV), with an affected depth exceeding 2.0 mm. Dislocation density analysis revealed a depth-dependent gradient across specimen cross-sections, with sample S1 (15 J) and S2 (30 J) showing 21 % and 8 % increases, respectively, in near-surface regions compared to untreated S0. Higher LSP energy (30 J) promoted sub-grain formation, leading to a reduction in dislocation density beyond a depth of 0.6 mm. The proportion of low-angle grain boundaries near the 0.36 mm surface exceeds 65 % in both LSP-treated specimens versus approximately 60 % in untreated S0. Surface topography analysis revealed a 2.65-fold increase in Ra value for the S2 (77 nm) compared to the S1 (29 nm). These findings offer valuable parametric optimization guidelines for LSP processing of LAM components that require controlled residual stress fields. The validated SWXRD technique presents a cost-effective method for industrial near-surface stress analysis.